The present invention relates to a method and apparatus for classifying solids and transporting solids-laden fluid containing large particle size solids which tend to plug a tubular fluid transport means and small particle size solids which will not plug the fluid transport means to thereby prevent such plugging. In a more particular aspect, the present invention relates to an improved heat exchange means adapted to transport a solids-laden fluid in indirect heat exchange with a heat exchange medium.
In many industrial operations, it is necessary to transport solids-laden fluid through tubular transport means. For example, in the fluid catalytic cracking of gas oils and/or topped crudes in a refinery, a slurry oil stream containing large size particles of contaminants, such as coke and tar, as well as residual amounts of small size particles of catalyst is separated from the reactor effluent. Normally, at least a portion of the slurry oil is cooled and recycled back to a separating zone in order to improve separation of desired products. Such cooling is normally carried out in a tube and shell type heat exchanger in which the slurry oil passes through the tubes of the heat exchanger while water is utilized as a cooling medium in the shell of the heat exchanger. Such cooling of the slurry oil serves the dual purpose of cooling the slurry oil as well as producing process steam from the cooling water. However, there is a tendency for large particles of contaminants, such as coke and tar, to plug the tubes of the heat exchanger thus eventually rendering the heat exchanger inefficient and eventually ineffective. At the present time, heat exchangers which have become plugged must be torn down and the tubes thereof reamed to remove the plugging solids and return the heat exchanger to its original efficiency. Obviously, this cleaning of the heat exchanger is costly and time consuming.
It would therefore be highly desirable to provide a method and apparatus whereby a solids-laden fluid containing large particle size solids which have a tendency to plug a tubular fluid transport means and small particle size solids which will not plug the transport means whereby the solids of large particle size are prevented from entering the tubular transport means while permitting the fluid containing the small particles to pass through the transport means. It would also be highly desirable to provide such a method and apparatus wherein a self-cleaning effect is produced.